Problem with K70 USB device connection on custom hardware ...

[Baerchen]

Hi,

I have an custome hardware based on a Kinetis K70 uC. The USB device is connected to the D+ and D- signals of the USB interface using a mini USB connector (the traces go straight from the connector to the chip pins). The custom hardware is almost identical to the K70 tower hardware.

I can run most of the MQX example programs on this board but run into a problem regarding the USB CDC-ACM example. When I plug the USB cable into the board, the JTAG interface unit LEDs go dark and my debugger in uVision crashes.

I double checked the connections, the lines are connected correctly. What I noticed is that the USB 5V input is not connected to VREGIN, instead it is connected to an GPIO for detecting a change.

Since connecting the USB seems so simple, what could be wrong? Dop I need to change the configuration since VREGIN is not conncted? Any advice is appreciated.

Thank you!

Frank

[apanecatl]

I believe the mcu is resetting, check the SRS registers to know the origin of the last reset source:

• RCM_SRS0
• RCM_SRS1

[Baerchen]

Hi Pedro,

why would the CPU go through reset in this situation? I will try it out.

My other question is, can the USB device interface work without having VREGIN connected?

Thank you.